/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.streaming.tests;

import org.apache.flink.api.common.functions.RichFlatMapFunction;
import org.apache.flink.api.common.state.ValueState;
import org.apache.flink.api.common.state.ValueStateDescriptor;
import org.apache.flink.api.common.typeinfo.BasicTypeInfo;
import org.apache.flink.api.common.typeinfo.TypeInformation;
import org.apache.flink.api.java.tuple.Tuple2;
import org.apache.flink.api.java.typeutils.ListTypeInfo;
import org.apache.flink.api.java.typeutils.TupleTypeInfo;
import org.apache.flink.configuration.Configuration;
import org.apache.flink.util.Collector;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Optional;

/**
 * This mapper validates sliding event time window. It checks each event belongs to appropriate number of consecutive
 * windows.
 */
public class SlidingWindowCheckMapper extends RichFlatMapFunction<Tuple2<Integer, List<Event>>, String> {

	private static final long serialVersionUID = -744070793650644485L;

	/** This value state tracks previously seen events with the number of windows they appeared in. */
	private transient ValueState<List<Tuple2<Event, Integer>>> eventsSeenSoFar;

	private transient ValueState<Long> lastSequenceNumber;

	private final int slideFactor;

	SlidingWindowCheckMapper(int slideFactor) {
		this.slideFactor = slideFactor;
	}

	@Override
	public void open(Configuration parameters) {
		ValueStateDescriptor<List<Tuple2<Event, Integer>>> previousWindowDescriptor =
			new ValueStateDescriptor<>("eventsSeenSoFar",
				new ListTypeInfo<>(new TupleTypeInfo<>(TypeInformation.of(Event.class), BasicTypeInfo.INT_TYPE_INFO)));

		eventsSeenSoFar = getRuntimeContext().getState(previousWindowDescriptor);

		ValueStateDescriptor<Long> lastSequenceNumberDescriptor =
			new ValueStateDescriptor<>("lastSequenceNumber", BasicTypeInfo.LONG_TYPE_INFO);

		lastSequenceNumber = getRuntimeContext().getState(lastSequenceNumberDescriptor);
	}

	@Override
	public void flatMap(Tuple2<Integer, List<Event>> value, Collector<String> out) throws Exception {
		List<Tuple2<Event, Integer>> previousWindowValues = Optional.ofNullable(eventsSeenSoFar.value()).orElseGet(
			Collections::emptyList);

		List<Event> newValues = value.f1;
		Optional<Event> lastEventInWindow = verifyWindowContiguity(newValues, out);

		Long lastSequenceNumberSeenSoFar = lastSequenceNumber.value();
		List<Tuple2<Event, Integer>> newWindows =
			verifyPreviousOccurences(previousWindowValues, newValues, lastSequenceNumberSeenSoFar, out);

		if (lastEventInWindow.isPresent()) {
			updateLastSeenSequenceNumber(lastEventInWindow.get(), lastSequenceNumberSeenSoFar, out);
		}

		eventsSeenSoFar.update(newWindows);
	}

	private void updateLastSeenSequenceNumber(
			Event lastEventInWindow,
			Long lastSequenceNumberSeenSoFar,
			Collector<String> out) throws IOException {
		long lastSequenceNumberInWindow = lastEventInWindow.getSequenceNumber();
		if (lastSequenceNumberSeenSoFar == null || lastSequenceNumberInWindow > lastSequenceNumberSeenSoFar) {
			lastSequenceNumber.update(lastSequenceNumberInWindow);
		} else if (lastSequenceNumberInWindow < lastSequenceNumberSeenSoFar) {
			failWithSequenceNumberDecreased(lastEventInWindow, lastSequenceNumberSeenSoFar, out);
		}
	}

	private void failWithSequenceNumberDecreased(
			Event lastEventInWindow,
			Long lastSequenceNumberSeenSoFar,
			Collector<String> out) {
		out.collect(String.format("Last event in current window (%s) has sequence number lower than seen so far (%d)",
			lastEventInWindow,
			lastSequenceNumberSeenSoFar));
	}

	/**
	 * Verifies if all values from previous windows appear in the new one. Returns union of all events seen so far that
	 * were not seen <b>slideFactor</b> number of times yet.
	 */
	private List<Tuple2<Event, Integer>> verifyPreviousOccurences(
			List<Tuple2<Event, Integer>> previousWindowValues,
			List<Event> newValues,
			Long lastSequenceNumberSeenSoFar,
			Collector<String> out) {
		List<Tuple2<Event, Integer>> newEventsSeenSoFar = new ArrayList<>();
		List<Event> seenEvents = new ArrayList<>();

		for (Tuple2<Event, Integer> windowValue : previousWindowValues) {
			if (!newValues.contains(windowValue.f0)) {
				failWithEventNotSeenAlertMessage(windowValue, newValues, out);
			} else {
				seenEvents.add(windowValue.f0);
				preserveOrDiscardIfSeenSlideFactorTimes(newEventsSeenSoFar, windowValue);
			}
		}

		addNotSeenValues(newEventsSeenSoFar, newValues, seenEvents, lastSequenceNumberSeenSoFar, out);

		return newEventsSeenSoFar;
	}

	private void addNotSeenValues(
			List<Tuple2<Event, Integer>> newEventsSeenSoFar,
			List<Event> newValues,
			List<Event> seenValues,
			Long lastSequenceNumberSeenSoFar,
			Collector<String> out) {
		newValues.stream()
			.filter(e -> !seenValues.contains(e))
			.forEach(e -> {
				if (lastSequenceNumberSeenSoFar == null || e.getSequenceNumber() > lastSequenceNumberSeenSoFar) {
					newEventsSeenSoFar.add(Tuple2.of(e, 1));
				} else {
					failWithEventSeenTooManyTimesMessage(e, out);
				}
			});
	}

	private void failWithEventSeenTooManyTimesMessage(Event e, Collector<String> out) {
		out.collect(String.format("Alert: event %s seen more than %d times", e, slideFactor));
	}

	private void preserveOrDiscardIfSeenSlideFactorTimes(
			List<Tuple2<Event, Integer>> newEvenstSeenSoFar,
			Tuple2<Event, Integer> windowValue) {
		int timesSeen = windowValue.f1 + 1;
		if (timesSeen != slideFactor) {
			newEvenstSeenSoFar.add(Tuple2.of(windowValue.f0, timesSeen));
		}
	}

	private void failWithEventNotSeenAlertMessage(
			Tuple2<Event, Integer> previousWindowValue,
			List<Event> currentWindowValues,
			Collector<String> out) {
		out.collect(String.format(
			"Alert: event %s did not belong to %d consecutive windows. " +
				"Event seen so far %d times.Current window: %s",
			previousWindowValue.f0,
			slideFactor,
			previousWindowValue.f1,
			currentWindowValues));
	}

	private Optional<Event> verifyWindowContiguity(List<Event> newValues, Collector<String> out) {
		return newValues.stream()
			.sorted(Comparator.comparingLong(Event::getSequenceNumber))
			.reduce((event, event2) -> {
				if (event2.getSequenceNumber() - 1 != event.getSequenceNumber()) {
					out.collect("Alert: events in window out ouf order!");
				}

				return event2;
			});
	}
}
